package lanqiao;

import java.util.Scanner;

public class test1 {
    //202
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        String str = scan.next();
        char[] chars = str.toCharArray();
        for (int i = 0; i < chars.length-1; i++) {

            for (int j = i+1; j < chars.length; j++) {
                if(chars[i]==chars[j]){
                    System.out.println("NO");
                    System.exit(0);
                }
            }
        }
        System.out.println("YES");
    }
}
